Look at your comment. Back to mine. Back to yours NOW BACK TO MINE. Sadly, it isn't mine. But if you stopped trolling and started posting legitimate crap it could LOOK like mine. Look down, back up, where are you? You're scrolling through comments, finding the ones that your comment could look like. Back at mine, what is it? It's a highly effective counter-troll. Look again, MY COMMENT IS NOW DIAMONDS.

We could go on for a while, going through every actual and potential implement that could be used for killing someone.

As a practical issue though, one can hardly dismiss that guns make it very easy to kill, and that is what they are intended for. Paperweights not so much. However, the cynic in me morbidly appreciates any implement that kills a decent number of people somewhere I'm not.

Though please keep them inside the asylum and ensure that anything intercontinental stays banned for private ownership.

The leading weapon for committing murder is guns. Therefore the issue at hand is guns if the aim is to prevent murder and other types of violence. You don't get the same effect with regulating rat poison, though if it becomes an issue you may wish to look into whether the regulation of it is sufficient.

Isn't the liberal justification for any regulation that it must be to prevent harm?

There is a strong correlation between the number of guns in a society and overall homicide rate. It is a lot harder, both physically and psychologically, to kill someone with a knife or anything other than a gun. While a regulation on guns wouldn't stop someone premeditated to murder, it would make it more difficult, and it would certainly reduce unpremeditated murders.

The Boston bombers may have been more successful with their bomb, though it doesn't mediate the fact that a hundred times more people have been killed and injured by guns in the days since. And I do believe bombs are illegal.